A synthetic aperture radar signal processing device which is mounted on a moving platform such as an aircraft or an artificial satellite includes a SAR sensor having an antenna. While repeatedly radiating electromagnetic waves during movement of the moving platform, the SAR sensor receives reflected echoes of the electromagnetic waves reflected by a target. The synthetic aperture radar signal processing device acquires a two-dimensional SAR image by performing signal processing on the received signal of the SAR sensor.
A process of acquiring a two-dimensional SAR image from a received signal of the SAR sensor is called an image reconstruction process. A processing method for the image reconstruction process is called an image reconstruction algorithm.
As the image reconstruction algorithm, for example, there is a backprojection algorithm disclosed in the following Patent Literature 1.
The backprojection algorithm is a method of acquiring a SAR image by calculating, for each pixel composing an image, a distance between the pixel and a moving platform, and extracting and integrating signals corresponding to the distance.
Hence, the backprojection algorithm has large computational load and requires a great amount of time for computations, in comparison with an image reconstruction algorithm (e.g., a range-Doppler algorithm or a polar format algorithm) where the amount of computation is reduced by collectively processing pixels composing an image.
The following Patent Literature 2 proposes a method of reducing computation time by performing received signal processing, a pulse compression process, and an image reconstruction process of a SAR sensor in a manner of a continuous work. In this method, however, since the amount of computation itself is not reduced, the number of computing machines to be used, etc., cannot be reduced.
In addition, since the method is premised on that the processes are performed in the continuous work manner after receiving a signal, it is difficult to apply a received signal observed in the past to an image reconstruction process using the backprojection algorithm.
A method disclosed in the following Non-Patent Literature 1 is a method of reducing the amount of computation of an image reconstruction process by performing an approximation calculation to obtain individual phase factors (i.e., phase factors for compensating for an error) which are used for the backprojection algorithm. In this method, a received signal observed in the past is able to be formed into an image using the backprojection algorithm.